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Xie C.-M.,Jilin University | Li C.,Jilin University | Wang M.,Jilin University | Wu Y.-W.,Aerospace Geophysical Survey and Remote Sensing Center for Land and Resources | Hu Z.-C.,Hubei University
Geological Bulletin of China | Year: 2014

Located between Amdo County and Nagqu County, the Nyainrong microcontinent is a EW-trending lenticular body in the middle of the Bangong Co-Nujiang River suture zone. The Nyainrong microcontinent is composed predominately of crystalline basement, Paleozoic strata, and Mesozoic granitoids. To better understand the Neoproterozoic tectono-thermal event in the Nyainrong microcontinent and constrain its tectonic evolution, the authors conducted detailed field observation, precise zircon U-Pb dating and geochemical study of the basement orthogneiss in the Amdo area. The field occurrence, mineral composition, textural characteristics, and whole-rock geochemical features of the three gneiss samples indicate that the protolith of the gneisses was intermediateacid intrusive rock. Gneiss zircon trace element tracing and genetic analysis show that the zircon has typical characteristics of magmatic zircon. The 206Pb/238U concordant ages of the zircon vary in the range of 820~843Ma, corresponding to the Neoproterozoic, which is the formation age of the protolith. Zircon saturation temperature estimates suggest that the initial temperatures of the magmatic source are 794~856℃, whereas the εHf(t) values are -0.8~0.5, 0.3 on average. The two-stage Hf-isotope model ages ((TDM2)) range from 1.58 to 1.96Ga. Combined with regional data, the authors hold that the tectonic setting of the Amdo gneiss protolith was closely related to the extensional environment resulting from stretching of the lithosphere. It is preliminarily considered that the Neoproterozoic magmatic events in the microcontinent might have resulted from the breakup of the Rodinia Supercontinent, with the tectonic setting possibly related to the breakup of the Yangtze plate continental margin. ©, 2014, Geological Bulletin of China. All right reserved. Source


Wang M.,Jilin University | Li C.,Jilin University | Xie C.-M.,Jilin University | Wu Y.-W.,Aerospace Geophysical Survey and Remote Sensing Center for Land and Resources | And 2 more authors.
Geological Bulletin of China | Year: 2014

There are widespread basic dykes and basalt distributed on the southern side of the Lungmu Co-Shuanghu-Lancang River suture zone trending nearly EW in southern Qiangtang. Basalts occur as interlayers in the Zhanjin Formation. Whole-rock compositions show that the southern Qiangtang basalts are alkaline and rich in Fe + Ti, and exhibit relative enrichment of light rare earth elements (LREE). Based on geochemical diagrams, the authors infer that the southern Qiangtang basalts erupted in an intraplate environment. It is concluded that the basalts in southern Qiangtang were related to the Permian mantle plume activity. The results achieved by the authors provide convincing evidence for the existence of the late Paleozoic mantle plume in southern Qiangtang. ©, 2014, Geological Bulletin of China. All right reserved. Source


Wu Y.-W.,Aerospace Geophysical Survey and Remote Sensing Center for Land and Resources | Wu Y.-W.,China University of Geosciences | Li C.,Jilin University | Xu M.-J.,Tianjin University | And 4 more authors.
Geological Bulletin of China | Year: 2014

In order to investigate the evolution of the Lungmu Co-Shuanghu plate suture zone and the tectonic history of central Qiangtang, the authors studied Guoganjianian ophiolite in the aspects of petrology, geochemistry and geochronology. The cumulate in Guoganjianian ophiolite was recently discovered during 1∶50000 regional geological survey of the Gemuri area. Geochemical studies show that the cumulate gabbro has low REE content and flatten REE patterns with slight enrichment of LREE, and the degree of differentiation between LREE and HREE is low. These samples are enriched in large ion lithophile elements (LILE) such as Rb and Ba, and depleted in Nb, Ta and Ti, suggesting that they were probably formed in a subduction zone. LA-ICP-MS technique was applied to U-Pb zircon dating of the cumulate gabbro from Guoganjianian ophiolite. The result shows that the ages of cumulate gabbro is 354.8Ma±2.4Ma, suggesting that Lungmu Co-Shuanghu Ocean already began its subduction in Early Carboniferous. The study of Guoganjianian cumulate gabbro provides important basic data for investigating the evolution of Lungmu Co-Shuanghu plate suture zone and the tectonic history of central Qiangtang. ©, 2014, Geological Bulletin of China. All right reserved. Source

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